fasteddie : Drive shaft vibration

Drive shaft vibration
Post by fasteddie on Aug 10, 2006, 6:48am

Having a drive line vibration problem on a M725 . Previous owner installed 78 J20 axles , TH400 trans with 76 IH transfer case . Truck had serious vibration when driving home from initial purchase . Drive shaft was cut too short and slip yoke was worn . Had new shaft made , that took care of most of the vibration. Still have some vibration on highway around 55MPH . Was wondering if anyone ran into this problem and if a CV joint on shaft like the short CJ's would solve this . This is a daily driver and it gets a little annoying .

Re: Drive shaft vibration
Post by gimpyrobb on Aug 10, 2006, 7:18am

The cv joints are for large angles at short distances, I doubt that would help anything.

Re: Drive shaft vibration
Post by alosix on Aug 10, 2006, 7:45am

After working on little jeeps and then seeing my M725 driveline there is no need for a CV (double cardon) on the rear at all.

I'd check:
1.) Out of balance driveshaft
2.) Dead/wearing ujoint
3.) Bad angles.

There's a good chance that when he did the swap he didn't get the rear pinion angle right. Is there any difference between accell and decel? I'd go grab and angle finder and check this.

Jason

Re: Drive shaft vibration
Post by fasteddie on Aug 10, 2006, 8:32am

Thanks , I was leaning towards drive shaft angle . Taking it to my shaft guy to check angles , since the shaft is 100% new , probably not worn parts . The CV joint was a thought that crossed my mind .

Re: Drive shaft vibration
Post by barrman on Aug 10, 2006, 9:38am

Check your front drive shaft as well. Even though it isn't transmitting power, it is still rotating and could cause a vibration. Since it is so easy, just pull it off one night and drive without the next day. You will probably notice a difference. I know mine looks good but, the lock out hubs reduced my vibration at speed enough for me to know when I have left the hubs locked in.

Re: Drive shaft vibration
Post by fasteddie on Aug 10, 2006, 10:09am

Pretty sure front shaft doen't turn , in 2H it's disengaged front transfer case , turns freely . Will remove it for a test . Also I do have lock out hubs which are disengaged.

Re: Drive shaft vibration
Post by alosix on Aug 10, 2006, 10:11am


Quote: <TABLE class=bordercolor cellSpacing=1 width="90%"><TBODY><TR><TD width="100%"><TABLE class=quote cellSpacing=0 cellPadding=2 width="100%"><TBODY><TR><TD width="100%">Pretty sure front shaft doen't turn , in 2H it's disengaged front transfer case , turns freely . Will remove it for a test . Also I do have lock out hubs which are disengaged.</TD></TR></TBODY></TABLE></TD></TR></TBODY></TABLE>

Unless it has lockout hubs on the front, it will probably spin in 2H because it will be driven by the front axle.

Jason